Trace Element Organic Speciation along the US GEOTRACES Pacific Meridional Transect

在海洋的许多地区，微生物生活的环境几乎没有它们生长和繁荣所需的营养。特别是，合成蛋白质和核酸所需的氮(N)、磷(P)和铁（Fe）等营养物质供应不足。从大陆吹来的灰尘向海洋提供铁，而在远离陆地的地区，海水中溶解的铁浓度极低，限制了微生物的生命。为了从周围环境中提取铁，一些微生物合成并释放一种叫做铁载体的有机化合物到它们的环境中。铁载体是专门设计来结合铁并将其运回细胞的。但直到最近，我们才有了测量海水中铁载体的技术，而且我们不知道它们在何时何地被使用，也不知道哪些微生物在制造和使用它们。这里提出的研究旨在解决所有这些问题。我们将沿着从阿拉斯加到塔希提岛的轨道测量太平洋中的铁载体。铁载体的分布将与其他测量数据（营养、细胞数量、基因组学）进行比较，以了解微生物如何能够在非常低铁的环境中生存，以及它们如何利用有机化合物从海水中提取金属。这项研究还将使我们能够测试和改进测量铁和其他金属（例如汞、铜和镉）与其他环境样本（例如地下水、湖泊和河流）中有机化合物结合的技术，这对监测金属污染物的毒性非常重要。几乎所有溶解在海洋中的铁都被成分未知的强有机配体络合。配体组成对微生物铁获取的影响尚不清楚，但使用模型配体的修正实验表明，它们可以促进或阻碍铁的吸收，这取决于它们的身份。在这里，我们建议测量一套生物活性微量元素（铁、铜、钴、镍和锌）配体（TE-Ls）在美国GEOTRACES太平洋经向样带（PMT）的颗粒和溶解有机物中的分子形态。我们将使用高压液相色谱耦合电感耦合等离子体质谱来检测和量化TE-Ls，并使用伴随的电喷雾电离体质谱来识别和表征有机配体。PMT将跨越5个不同的生物地球化学省：陆架/斜坡、亚北极高营养/低叶绿素（HNLC）、北太平洋少营养环流、赤道HNLC和南太平洋少营养环流。巡航轨道进一步相交至少三个不同的地下特征，亚北极和赤道粒子面纱，缺氧水域和中深度热液羽流。我们预计，这些制度和特征的独特物理、化学和生物特性将导致水柱上下的TE-L分布非常不同。TE-L分子物种形成测量将使我们能够更好地将微量元素分布数据集与地球上一些地区微生物代谢营养驱动变化的宏基因组数据集结合起来。S主要生物群系。

In many areas of the ocean microbes live in an environment that has very little of the nutrients they need to grow and thrive. In particular, nutrients with nitrogen (N), phosphorus (P), and iron (Fe), needed for the synthesis of proteins and nucleic acids, are in short supply. Iron is supplied to the ocean by dust blowing off the continents, and in areas remote from land, microbial life is limited by the very low concentrations of iron dissolved in seawater. To extract iron from their surroundings, some microbes synthesize and release organic compounds called siderophores into their environment. Siderophores are specifically designed to bind iron and transport it back into the cell. But only recently have we had the technology to measure siderophores in seawater, and we do not know where or when they are used, or which microbes are making and using them. The study proposed here is designed to address all of these questions. We will measure siderophores in the Pacific Ocean along a track from Alaska to Tahiti. The distribution of siderophores will be compared with data from other measurements (nutrients, cell numbers, genomics) to understand how microbes are able to live in very low iron environments, and how they can use organic compounds to extract metals from seawater. The study will also allow us test and improve the technology of measuring iron and other metals (mercury, copper, and cadmium, for example) bonded to organic compounds in other environmental samples, such as ground-waters, lakes and rivers, which is important for monitoring the toxicity of metal contaminants. Nearly all iron dissolved in the ocean is complexed by strong organic ligands of unknown composition. The effect of ligand composition on microbial iron acquisition is poorly understood, but amendment experiments using model ligands show they can facilitate or impede iron uptake depending on their identity. Here we propose to measure the molecular speciation of a suite of bioactive trace element (iron, copper, cobalt, nickel, and zinc) ligands (TE-Ls) in particulate and dissolved organic matter across the US GEOTRACES Pacific Meridional Transect (PMT). We will use high pressure liquid chromatography coupled to inductively coupled plasma mass spectrometry to detect and quantify TE-Ls, and companion electrospray ionization mass spectra to identify and characterize organic ligands. The PMT will cross five different biogeochemical provinces: shelf/slope, subarctic high nutrient/low chlorophyll (HNLC), North Pacific oligotrophic gyre, equatorial HNLC, and South Pacific oligotrophic gyre. The cruise track further intersects at least three different subsurface features, the subarctic and equatorial particle veils, oxygen deficient waters, and mid depth hydrothermal plumes. We expect the unique physical, chemical, and biological properties that characterize these regimes and features will lead to very different TE-L distributions across and down the water column. TE-L molecular speciation measurements will enable us to better integrate datasets of trace element distribution with metagenomic datasets of nutrient-driven changes in microbial metabolism across some of the Earth?s major biomes.